Macrochoecilla Chavtur, 2018

Chavtur, Vladimir G. & Bashmanov, Alexander G., 2018, Pelagic ostracods of the new subtribe Conchoeciina (Ostracoda, Crustacea) from the North Pacific, Zootaxa 4516 (1), pp. 1-127 : 49-51

Macrochoecilla Chavtur , gen. nov.

1906 Conchoecia Magna-Gruppe—Müller: 98–99 (partly);

1909 Conchoecia zetesios (immature instars)—Fowler: 254.

1968 Conchoecia Magna-Groupe—Deevey: 76–77 (partly);

1973 Conchoecia— Poulsen: 123–124 (partly);

1979 Conchoecia— Martens: 317 (partly);

2012 Conchoecia— Drapun & Smith: 53 (partly).

Type-species. Conchoecia macrocheira Müller, 1906

Etymology. The name is derived from the Latin specific name “macrocheira” and “-oecilla” derived from the Greek word “oɩĸoσ” meaning house, from which the terms ecology and economy have been derived, and is the ending that has become standard for the Conchoeciinae genera.

Composition. This genus is monospecific, consisting of only Macrochoecilla macrocheira ( Müller, 1906) comb. nov.

Diagnosis of genus. Adult male. Carapace. The length is between 2.70–3.40 mm. The height is greatest at the anterior end. Locations of the asymmetrical glands are usual for the subtribe. Lateral corner glands are missing.

Frontal organ. The capitulum is bent downwards and has a rounded tip.

First antenna. Armature of seta-e consists of a comb of about 26–35 pairs of slender and relatively long spines directed proximally.

Second antenna. Seta-b of the endopodite has between five and twenty long, posterior, fine filaments and between zero and four medium-length anterior filaments. The right clasping organ is slim, usually almost square or slightly acute-angled. The left clasping organ is right-angled, and like the right organ, has a pointed tip.

Mandible. The lateral tooth on the basale endite is absent. The epipodite has no setae or a verruca. The ventral margin of the first endopodite segment bears two long setae.

Maxilla. Anterior setae are placed close together near the end of the first endopodite segment.

Sixth limb. The ventral margin of the basale has five plumose setae.

Caudal furca. An unpaired seta is present.

Copulatory limb. It is elongated, widest at the middle, tapering to an obliquely rounded tip.

Adult female. Carapace. The length is between 3.20–4.10 mm. It is sub-rectangular, with rounded corners and not tapered anteriorly. The carapace is more rounded than in the male.

Frontal organ. The capitulum is very long, clearly curved, downward pointing, fused with the stem and has a rounded tip.

First antenna. The dorsal seta on the second segment is well developed. The anterior margin of seta-e is bare.

Second antenna. The first endopodite segment is about 27%, 37–38% and 50–51% the lengths of setae-g, -f and –h, respectively.

Mandible, maxilla and caudal furca are similar to those of the male.

Sixth limb. The basale has five ventral, long, plumose setae and without or with one lateral, long, plumose seta.

Description of genus. Adult male. Carapace. The length is between 2.70–3.40 mm. The greatest height is in the anterior region, and is over half of the length. Shoulder vaults are well developed. The anterior margin beneath of the rostral incisures is swollen. The posterior margin is almost straight. The ventral margin has a slightly or noticeable concavity. The left asymmetrical gland is slightly moved anteriorly and the right asymmetrical gland is located at the postero-ventral corner. There are no lateral corner glands or gland cells below the incisures. Sculpture is either lacking or only weakly developed on the anterior part of the carapace.

Frontal organ. The stem is straight. The capitulum is bent downwards. In the male it is angled down at about 45°. The capitulum is relatively slim, slightly concave anteriorly, with a rounded tip and is almost completely covered with small spines.

First antenna. The first and the second segments are either subequal or the first is slightly shorter. Seta-a barely reaches or just extends beyond the suture between the first and the second segments of the limb. Seta-c is very long, about 1.5–2.5 times as long as the combined lengths of the third, fourth and fifth segments. Armature of seta-e consists of a comb of about 26–35 pairs of slender, relatively long spines directed proximally.

Second antenna. Seta-b of the endopodite has between five and twenty long proximal fine filaments and between zero and four medium-length distal filaments. The right clasping organ is slim, almost square or slightly acute-angled. The left clasping organ is right-angled, and like the right organ has a pointed tip.

Mandible. The lateral tooth on the basale endite is absent. The epipodite is without setae or a verruca. The ventral margin of the first endopodite segment has two long setae. The disto-dorsal seta of this segment is usually bare but rarely can have small spines. The masticatory pad consists of four small flaps (the distal margin of which has rather long papillae), with four flat, broad, blunt spines and 90–120 seta-like filaments.

Maxilla. The first endopodite segment has six anterior setae and three posterior setae. All setae are with rather long and strong spines. The anterior setae are placed close together near the distal end of the segment. Along the distal edge of this segment is a line of five to eight long spines.

Fifth limb. The basal segment has a proximal group of three setae ventrally, a medio-lateral group of two and a distal group of three setae. The basal segment lacks a lateral seta, but dorsally has a long distal seta (vestige of the exopodite), that extends just beyond the end of the limb. The first endopodite segment bears two ventral setae and one dorsal seta.

Sixth limb. The coxale has two long, plumose setae (one of which somewhat shorter). The ventral margin of the basale bears five plumose setae (but Poulsen 1973 illustrates the three distal setae as being bare). The exopodite seta is short, only reaching to the end of the first endopodite segment.

Caudal furca. Each lamella has eight pairs of slim claws. An unpaired seta is present.

Copulatory limb. It is elongated, widest at the middle, and tapering to an obliquely rounded tip. The appendage is broad or relatively narrow and rounded. The distal seta is very thin. The limb has seven oblique muscle bands.

Adult female. Carapace. The length is between 3.20–4.10 mm. The carapace is sub-rectangular, with rounded corners and does not taper anteriorly. The height is close to half the length. The locations and numbers of glands are similar to the male’s (with exception of the dorso-medial glands). The carapace is more rounded than in the male. The postero-dorsal corner is rounded. The posterior margin is more or less strongly arched. The ventral margin is concave. Sculpture is similar to that of the male.

Frontal organ. The capitulum is very long, clearly curved downward, and fused with the stem. It is longer than the stem and almost completely covered with small spines; the tip is rounded.

First antenna. The dorsal seta on second segment is well developed. Setae-a–d are a little longer than the shaft of the limb. Seta-e has a bare anterior margin.

Second antenna. The first endopodite segment is about 27%, 37–38% and 50–51% the lengths of setae-g, -f and –h, respectively. Terminal setae on the endopodite are slightly tapering towards the pointed tip.

Mandible, maxilla and caudal furca are similar to those of the male.

Sixth limb. The coxale has two very long, plumose setae. The basale bears five ventral long, plumose setae and without or with one lateral long, plumose seta. The exopodite reaches 2/5 the length of the first endopodite segment.

Comparison ( Table 2).The new genus clearly differs from all the other genera of this tribe in many respects: the large size of the carapace, the structure of the capitulum of the frontal organ in the female with a rounded tip, the large size and slimness of the male’s right clasping organ on the second antenna, the lack of a lateral tooth on the basale endite of the mandible and the absence of a verruca and seta on the mandibular epipodite, with two long setae on the ventral margin of the first endopodite segment, and with four small elongated flaps placed beside one another (distal margins of which have rather noticeable papillae).

Distribution. Since the genus Macrochoecilla is monospecific its distribution is same as for M. macrocheira (see below).